Conventionally, threaded connections between oilfield tubulars and similar conduits, pipes, and/or other engageable members are formed by providing a large torque to complimentary male and female threaded members. The magnitude of the force used to form the connection can vary depending on the dimensions and/or tolerance of the members. During use, conduits used to contain fluid flow must be connected using a torque sufficient to form a fluid-tight seal therebetween. Conduits that must withstand significant fluid pressures, such as drill pipe and other oilfield tubulars, require a significant torque (up to 50,000 foot-pounds, or more) to form such a seal. Even when properly torqued, multiple, redundant seals are often required to ensure integrity under anticipated fluid pressures without permitting damage to the components.
Application of significant torque to conventional tubular components can cause galling, stripping, and/or cross-threading of the threads. Galling and similar destructive deformation can create difficulty when attempting to disengage a threaded connection, and can prevent reuse of the deformed tubular components. Typically, to reduce and/or prevent galling, tubular threads must be treated, such as through application of a coating of tin, zinc, or other metals and/or alloys, or by “sugar blasting” the threads with fine grains of sand. Additionally, many tubular components utilize specialized thread configurations, having thread and/or stab flank and load flank angles selected to reduce galling while maintaining intimate contact between associated threaded portions, and allowing for radial expansion of the connection. When a threaded connection is placed under a significant lateral and/or bending force, such as when used within a directional borehole, one or more of the threads can become disengaged, hindering the integrity of the connection and seal. Buttress threads having a negative load flank angle can be used to facilitate retaining the connection between threaded components.
A need exists for a coupling having a configuration of sealing surfaces that provides a fluid-tight integrity exceeding that of conventional threaded connections.
A need also exists for a coupling having a configuration of components that enables a connection to be formed without galling or damaging the mechanical strength of the threads or otherwise undesirably deforming any of the components, while maintaining the fluid-tight integrity and stability of the threaded connection.
A further need exists for a coupling having a configuration that allows for radial expansion of components without causing damage or undesired deformation of the components, or hindering the integrity of the connection.
Embodiments of the present invention meet these needs.